Apparatus for vapor coating



Jan. 5, 1954 F. w. SCHULER APPARATUS FOR VAPOR COATING Filed May 12, 1952 AC Supply INVEN TOR.

FREDERIC W. SCHULER UMM ATTORNEY Patented Jan. 5, 1954 APPARATUS FOR VAPOR COATING Frederic W. Schuler, Cambridge, Mass,

assignor to National Research Corporation, Cambridge, Mass, a corporation of Massachusetts Application May 12, 1952, Serial No. 287,355

3 Claims. 1

This invention relates to coating and more particularly to the continuous coating of flexible substrates with a metal such as aluminum by the vapor deposition of the aluminum on the substrate.

A principal object of the present invention is to provide coating processes and apparatus capable of operating for long periods of time with a high coating rate.

Another object of the present invention is to provide such apparatus and processes having a high degree of reliability and utilizing cheap materials in the source of aluminum vapors.

Still another object of the invention is to provid an apparatus of the above type which is particularly adapted to the continuous coating of wide substrates at high rates of speed.

Still another object of the invention i to provide improvements in the coating processes and apparatus shown in the cop'ending applications of Clough et al., Serial No. 171,432, filed June 8Q, 1950, and Schuler et al., Serial No. 254,936, filed November 5, 1951.

Other objects of the obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others, and th apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be in dicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

Fig. 1 is a diagrammatic, schematic, sectional view of one continuous coating apparatus em- I bodying the present invention;

Fig. 1a is an enlarged, fragmentary view of a portion of Fig. 1; and

Fig. 2 is a sectional view taken along the line 22 of Fig. 1.

In the present invention a metal such as aluminum is evaporated under a high vacuum (preferably less than .601 mm. Hg abs.) and the aluminum vapors are condensed on a flexible substrate which is moved past the source of aluminum vapers. In the evaporation of aluminum it is desired that the aluminum be at a high temperature (preferably above about 1300 C.) and that the aluminum have a large effective evaporating area. It is also desirable that all invention will in part be hot areas of the aluminum vapor source which do not vaporize aluminum be shielded from the substrate so that these hot areas do not transmit radiant heat to the substrate. Additionally, such a source should be cheap, should be capable of operating for relatively long periods of time, and should be capable of generating a stream of aluminum vapors, which is relatively uniform, across the substrate passing over the source. The rate of evaporation from the source should be relatively steady and it should be substantially uniform over the whole area thereof.

These highly desirable objectives are achieved in the present invention by providing, as a source of aluminum vapors, an elongated hollow carbon member extending generally across the path along which the substrate moves in the vacuum coating chamber. This hollow elongated member has a groove in the top thereof for confining a shallow, elongated pool of molten high temperature aluminum. This hollow member is preferably a cylindrical dense carbon rod and preferably includes at least a surface stratum which is wettable by molten aluminum, and which is substantially inert to molten aluminum. In a preferred embodiment this surface stratum comprises a carbide in the class consisting of the carbides of titanium, Zirconium, hafnium, vanadium, columbium, and tantalum. Inside of the elongated hollow carbon rod is a heater element adapted to be heated to a relatively high temperature and to heat the outer carbon element by transfer of radiant heat to the inner surface thereof. From the standpoint of reliability and cheapness, this heater element is preferably a graphite rod which is heated by its own resistance to a temperature on the order of 2000 C. or above. This inner graphite rod is maintained electrically insulated from the inner walls of the outer carbon rod, preferably by being physically spaced from these inner walls. This arrangement provides indirect high temperature heating of the outer carbon rod so that this outer carbon rod remains at a high temperature on the order of 1300" C. to 1508" C. This high temperature evaporates the aluminum which vie-ts substantially all of the surface of the outer rod which is in position to radiate heat to the substrate moving therepast.

Referring now to the drawing there is shown one preferred apparatus embodying the present invention. In the figures, id represents a vacuum-tight housing defining therewithin a vacuum. coating chamber L? which is arranged to be evacuated to a low-free-air pressure, on

the order of less than 1 micron Hg abs, by means of a vacuum pumping system schematically indicated at !4. Within this chamber the substrate it to be coated is guided from a supply H thereof past a plurality of cooled guiding rolls 1% to a take-up spool i9. During the passage from supply H to take-up spool [9, the substrate it travels in a series of convolutions near a source 23 of aluminum vapors. This general arrangement of substrate feed and guiding rolls is similar to that illustrated in the above mentioned Schuler et al. application, Serial No. 254,936. As shown more clearly in Fig. 2, the source 20 preferably comprises an elongated, hollow, dense carbon rod 22 and a slightly longer graphite heater rod 23 passing through the interior of the hollow carbon rod 22. In the upper surface of the outer rod 22 there is provided an elongated groove 24 into which solid aluminum, in the form of a wire 26, is fed, this groove '24 serving to confine a shallow elongated pool of molten, high temperature aluminum. As illustrated in Fig. 2, aluminum is fed to both ends of the rod 22, aluminum wires 25 being illustrated for this purpose. A second pair of wires 27 is also fed to the groove 24, these second wires, which may be formed of titanium, being fed immediately adjacent the points of feed of the aluminum wires 26.

The inner graphite rod 23 is supported by a pair of water-cooled grips 28 having cooling coils 3E] embedded therein. Carbon spacing elements 3! are provided between the water-cooled grips 28 and the rod 23'. The grips 28 may be physically supported by water-cooled pipes 32, these pipes also serving, in a preferred embodiment, as electrical leads for supplying high amperage, low voltage current to the heater rod 23. A similar arrangement of water-cooled grips 34, cooling passages 36, and supporting tubes 38 is provided for supporting the outer hollow carbon rod 22. In a preferred embodiment of the invention, the two rods are supported, as illustrated, in such a manner that these rods are out of contact throughout their length, thus being electrically insulated from each other. As a result of this arrangement, the outer hollow rod '22 is maintained electrically neutral, while the inner graphite rod 23 carries all of the heating current. Power leads 39 preferably connect the graphite heater rod 23 to a source of high amperage, low voltage power schematically indicated as a transformer 49.

Aluminum 26 is preferably supplied from a pair of wire coils 42 thereof, while the second pair of wires Z'i' (e. g., titanium) are fed from coils 44 thereof. Two pairs of wire-feeding mechanisms 46 are provided for feeding the two pairs of wires adjacent the ends of the trough 24. These wire-feeding mechanisms include wire-guiding tubes 2! and are arranged so that the aluminum wire 25 is fed at a much faster rate, by weight, than the titanium wire 21. This aspect of the invention is described and claimed more fully in the copending application of Schuler et al. mentioned above.

In one preferred form of the invention, the hollow carbon rod 22 is formed of Becker Bros. B-4 carbon. This rod may be about 1.5 inches in diameter, about '7 inches long (6 inches effective evaporating length), and may have a groove in the top thereof which is inch wide by about inch deep. Such a rod may have a hole extending longitudinally thereof which is slightly eccentric and approximately 1 inch in diameter. The inner heater rod 23 is preferably Becker Bros. graphite grade C-4 of approximately /2 inch or inch diameter. As shown, this graphite heater rod is slightly longer than the outer carbon rod. In order to prevent radiant heat transfer from the exposed ends of the heater rod 23, a heat shield 58 is provided adjacent each end of the rod 23.

In the operation of the device shown in the drawing, roll ll of the substrate I6 is positioned within the vacuum chamber l2. The substrate is guided around the various rolls l3 and is connected to the take-up spool IS. The two spools of aluminum wire 42 are positioned so that the ends thereof may be fed through their respective Wire-feeding mechanisms 46 and through their Wire-guiding tubes 4?. The two spools of titanium wire are similarly fed through the wire-feeding mechanisms 45 and their guiding tubes 41. Cooling water, or other refrigerant (at about 40 F. or lower), is then circulated through the cooling rolls i8 by suitable piping (not shown) so as to chill the rolls I8. Cooling water is also circulated through the pipes 32 and 38 and the channels as and 35 in the various rod holders. In those cases where the outer rod 22 is an uncoated carbon rod, pieces of solid aluminum and solid titanium, for example, may be inserted in the groove 24, as described in the above mentioned Schuler et al. patent application.

Vacuum chamber i2 is then evacuated to a low-free-air pressure (on the order of 1 micron Hg abs.) by vacuum pumping means [4. When the requisite low pressure is achieved, the inner rod 23 is heated to a high temperature (on the order of 2000 C. or above) by passing current therethrough. The radiant heat transferred from the inner rod 23 to the outer hollow rod 22 rapidly heats the outer rod to a sufiiciently high temperature so that the aluminum in the trough 24 is melted, thereby dissolving the solid titanium and forming a titanium carbide surface on the outer rod 22. This titanium carbide surface extends over substantially the whole outside of the carbon rod 22 to provide a large area which is wettable by molten aluminum. This wetting of the molten aluminum is shown best in Fig. 1a. Due to the high temperature of the inner graphite heater rod 23, the outer carbon rod 22, and the aluminum carried thereby, is rapidly raised to a high temperature, on the order of 1300 C. to 1500 C., so that the aluminum is evaporated therefrom at a. high rate of speed. Since the aluminum is rapidly evaporated, additional aluminum and additional titanium, in the form of the wires 26 and 21, are fed to the trough by the feeding mechanisms 46 so as to maintain the groove 24 substantially completely filled with molten aluminum. This provides that there is at all times sufllcient molten aluminum available to wet substantially all surfaces of the outer rod 22 which are in position to radiate heat to the substrate.

When the aluminum on the surface of the outer rod 22 has been heated to a high temperature, on the order of 1300 C. to 1500 C., the substrate is moved above the rod so that the substrate becomes coated by the aluminum vapors emanating from the rod. It is desirable that the substrate not be exposed to vapors coming from the rod until these vapors have reached a relatively high temperature so as to prevent undue transfer of radiant heat to the substrate. To achieve this purpose a shield (not shown) may be positioned over the aluminum source during the initial heat-up period, this shield being removed when the proper high temperature has been attained.

As explained in the above mentioned Clough et al. application and the Schuler et al. application, it is highly desirable that there be provided on the outer rod a surface stratum of a carbide selected from the group consisting of the carbides of titanium, zirconium, hafnium, vanadium, columbium, and tantalum. This carbide may be formed on the surface of the rod prior to insertion of the rod in the coating chamber. However, it is preferred, as mentioned in the schuler et al. application, to form this carbide surface by initially providing one of the above metals in the groove at the top of the rod when the initial charge of aluminum is melted therein. It is also desirable that a second metal, such as zirconium, titanium, or tantalum, be fed along with the aluminum so as to prevent local erosion by the freshly fed aluminum at the point of feed. When this type of metal is fed to the rod along with the aluminum, it is found that the carbides of molybdenum and tungsten may be equally used as initial coatings on the rod. This second metal can be in the form of an aluminum alloy or as a separate wire fed along with the aluminum wire, as explained and claimed more fully in the above mentioned schuler et al. application.

While one preferred method of insulating the inner rod from the outer rod has been illustrated, other techniques may be employed, and a refractory insulating material may be provided between these two rods. The control of feed of aluminum to the rod may be achieved visually by the operator during the coating operation.

In general, it is desired that the outer rod be formed of a dense carbon or a dense mixture of carbon and graphite. The inner rod is preferably formed of graphite, since graphite has the requisite structural strength at the high temperatures involved and is relatively cheap.

Since certain changes may be made in the above process and apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for coating a substrate with aluminum by vacuum evaporating said aluminum on said substrate, said apparatus comprising a vacuum chamber, means providing a source of aluminum in said vacuum chamber, means for evacuating said chamber, an elongated hollow member having an elongated groove along the top thereof positioned within said chamber, said member having a surface wettable by molten aluminum, means for feeding aluminum from said source thereof to said hollow member at a rate sufiicient to keep said groove substantially completely filled with molten aluminum, said Wettable surface on said member assuring coverage by molten aluminum of a substantial portion of said member in addition to said groove, a heater rod inside of said hollow member, means for electrically insulating said heater rod from said hollow member, means for supplying electric current to said heater rod to raise the temperature thereof to about 2000 C. and above, and means for passing said substrate over said member to coat said substrate with aluminum.

2. Apparatus for coating a substrate with aluminum by vacuum evaporating said aluminum on said substrate, said apparatus comprising a vacuum chamber, means providing a source of aluminum in said vacuum chamber, means for evacuating said chamber, means for guiding said substrate in a predetermined path through said vacuum chamber, a generally cylindrical hollow carbon element extending horizontally and transversely of the path of substrate travel, said carbon element having an elongated groove in the upper surface thereof, means for feeding aluminum from said source thereof to said hollow member at a rate sufiicient to keep said groove substantially completely filled with molten aluminum, said wettable surface on said member assur ing coverage by molten aluminum of a substantial arcuate portion of said member in addition to said groove, a graphite heater rod extending through the hollow carbon element, means for supporting said graphite rod and said carbon element so that they are out of contact throughout their length, means for supplying electric current to said heater rod to raise the temperature thereof to about 2000 C. and above, and means for passing said substrate over said member to coat said substrate with aluminum.

3. Apparatus for coating a substrate with metal by vacuum evaporating said metal on said substrate, said apparatus comprising a vacuum chamber, means providing a source of metal in said vacuum chamber, means for evacuating said chamber, means for guiding said substrate in a predetermined path through said vacuum chamber, a generally cylindrical hollow carbon element extending horizontally and transversely of the path of substrate travel, said carbon element having an elongated groove in the upper surface thereof, means for feeding metals from said source thereof to said hollow member at a rate sufiicient to keep said groove substantially completely filled with molten metal, said wettable surface on said member assuring coverage by molten metal of a substantial arcuate portion of said member in addition to said groove, a graphite heater rod extending through the hollow carbon element, means for supporting said graphite rod and said carbon element so that they are out of contact throughout their length, means for supplying electric current to said heater rod to raise the temperature thereof to about 2000 C. and above, and means for passing said substrate over said member to coat said substrate with metal.

FREDERIC W. SCHULER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,153,786 Alexander et al Apr. 11, 1939 2,282,098 Taylor May 5, 1942 2,382,432 McManus et al. Aug. 14, 1945 2,450,856 Colbert et a1 Oct. 5, 1948 2,557,530 Bancroft June 19, 1951 

1. APPARATUS FOR COATING A SUBSTRATE WITH ALUMINUM BY VACUUM EVAPORATING SAID ALUMINUM ON SAID SUBSTRATE, SAID APPARATUS COMPRISING A VACUUM CHAMBER, MEANS PROVIDING A SOURCE OF ALUMINUM IN SAID VACUUM CHAMBER, MEANS FOR EVACUATING SAID CHAMBER, AN ELONGATED HOLLOW MEMBER HAVING AN ELONGATED GROOVE ALONG THE TOP THEREOF POSITIONED WITHIN SAID CHAMBER, SAID MEMBER HAVING A SURFACE WETTABLE BY MOLTEN ALUMINUM, MEANS FOR FEEDING ALUMINUM FROM SAID SOURCE THEREOF TO SAID HOLLOW MEMBER AT A RATE SUFFICIENT TO KEEP SAID GROOVE SUBSTANTIALLY COMPLETELY FILLED WITH MOLTEN ALUMINUM, SAID WETTABLE SURFACE ON SAID MEMBER ASSURING COVERAGE BY MOLTEN ALUMINUM OF A SUBSTANTIAL PORTION OF SAID MEMBER IN ADDITION TO SAID GROOVE, A HEATER ROD INSIDE OF SAID HOLLOW MEMBER, MEANS FOR ELECTRICALLY INSULATING SAID HEATER ROD FROM SAID HOLLOW MEMBER, MEANS FOR SUPPLYING ELECTRIC CURRENT TO SAID HEATER ROD TO RAISE THE TEMPERATURE THEREOF TO ABOUT 2000* C. AND ABOVE, AND MEANS FOR PASSING SAID SUBSTRATE OVER SAID MEMBER TO COAT SAID SUBSTRATE WITH ALUMINUM. 